Most energy produced today is derived from fossil fuels such as oil, coal and natural gas. However, these energy sources all have significant disadvantages including pollution, periodic shortages and escalating costs of extracting the fuels.
By contrast, solar, wind and hydroelectric energy systems all offer the advantages of being relatively safe and reliable. Moreover, these technologies have the common advantage of drawing their power from sources that are virtually inexhaustible. However, this is not to say these technologies are without difficulties. One difficulty with these technologies is that the underlying energy sources i.e., wind, sunlight and water can be subject to periodic swings in availability, e.g., the sun may eclipse, the winds may subside, and water levels may fall due to extended periods of drought. Another difficulty is that the best locations for capturing the foregoing energy sources are often remote from where the energy is used. This is especially the case for large-scale hydropower installations. The location of hydropower installations is generally in proximity to a large body of water. An example of a large body of water is a reservoir fed by a river. Most of the remote locations near large bodies of water are already in use i.e., future growth of hydropower installations is limited.
Traditionally, most wind, solar and hydropower installations (particularly large scale, commercial operations) rely on utility grids for transferring the generated energy to where it will be used. This may not be the most efficient use of the generated energy from an economic standpoint. As is well known, connecting a wind or hydro powered turbine generator to a utility grid imposes certain constraints on the generator. For example, the power output of the generator must be synchronized (i.e., in phase) with the utility's grid supply. With synchronized generators, this is accomplished by controlling the rotor speed of the turbine to exactly match the utility supply frequency. Another constraint with relying solely on a utility grid, as a carrier of generated, energy is that there may be a low demand on the grid at the same time there is ample capacity to generate additional power. When this occurs, the energy that could be captured is simply wasted. Although various energy storage systems (e.g., battery storage, compressed hydrogen fueling tanks or pumped hydro-energy storage) can be utilized to overcome this problem. Such systems are relatively expensive to install and result in efficiency losses of their own due to the repeated energy conversions.